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Finally put the TCD1304 linear CCD driver onto my XC7Z020 board. The IP core provides an AXI-Lite interface for register access to adjust the CCD driving parameters in realtime. It also offers a high-speed AXI-Stream port for CCD reading output. Connecting the AXI-Stream port to an AXI-Data FIFO IP followed by a Xilinx VDMA IP, we can automatically save frames into a pre-allocated memory pool which act as a frame buffer. Thanks to the VDMA IP core, I can quickly get informed from the linux side when buffer is ready and get synced with the CCD driver.

I have got a Z-turn board (designed by Myir Technology) equipped with XC7Z020 SoC chip.

To briefly introduce the ZYNQ devices, we can define it as a combination of FPGA and a dual-core ARM Cortex-A9 processor(also called hard core compared to soft core like MicroBlaze) with on-chip programmable interconnection. The internal connection make the data transfer easier and faster than the previous scheme that place an external ARM processor near a FPGA chip. In the ZYNQ scheme, they call the ARM part Processing System(PS), and the FPGA part Processing Logic(PL). Many convenient implementation of AXI4 bus is provided by Xilinx as IP cores. With the block design function in Vivado, we can quickly integrate our IP cores into the system. Also thanks to the powerful ARM core, we can run Linux operating systems on the PS and directly control all the hardware implementation on the PL.

In Xilinx devices, the clock can be generated by a module called Mixed-Mode Clock Manager(MMCM), which includes a PLL. This module have fractional multiplier and divider thus is quite versatile to meet any need for digital clock generation. Another good thing is that it can be dynamically reconfigured through a set of registers.

The MCMM_DRP is connected to the PS GP0 port through an AXI-interconnection module. I have allocated a small 4KB virtual space for the registers starting at 0x40000000(which is right after my 1GB DDR3 RAM). Because of the limited bandwidth of my Mini-DSO, I have put a 1/4096 clock divider at the output.

In the Linux side, I have two choices to make modifications on registers. The first way is to write a kernel driver that well handles the requests from user space and do the reconfiguration on registers. However, this is not so easy to implement. The another way is to use mmap to map the registers to a virtual address and modify that. This way is easy and can be done in the user space(root privilege is required, though), but not safe. As a simple test and our ‘Hello world!’ project to ZYNQ, I chose the second plan.

There are bunches of frameworks to support a graphical user interface (GUI) on your python application. I choose to use wxPython because I was familiar with that. I embed the graph generated by matplotlib into the GUI to give realtime updating of the data.

This application uses a HighFinesse wavelength meter monitoring a Rubidium locked laser and a commercial He-Ne laser. It can automatically record data into a file and calculate the deviation. A round-robin buffer is used to show short-term and long-term data.

I write all the code needed to drive this printer. The program is running on an Arduino DUE board. The controller is equipped with a control pad and a LCD display. It can simultaneously drive 4 step motors and handle 3 channel of temperature PID. 3D data can be saved into SD card and read by the printer offline or directly sent by a computer.